im not too sure about it, but i think hugging the ground clutter
might disrupt the Missile's guidance system... and if its only at
1k ft, i bet the SAM will climb faster.
on the note of heading of the airplane... a head on shot would mean
the missile closes a lot faster as the missile and the plane both ,
which equals less time for the pilot to react.
Conversely, should the pilot do eratic evasive
manouvres/countermeasures and this doesnt give the missile much
chance to react either and should it fail to hit the first time
round, it has to execute a full 180 degree turn, in the process
reducing range and speed.
Furthermore, only All-Aspect missiles are able to track a head-on
target (eg. mistral)
If its a tail-chase, the aircraft has the advantage of distance
between itself and the missile, which means the missile has to be
able to close in fast enough and cover the distance seperating it
and the already afterburning airplane (thus reduced effective
range) while not being fooled by chaff, flares, ecm...
On the side note, it can better react to the pilots, evasive
manouvers... and all missile types are effective not just
All-Aspect